How to use Python dataclasses

Everything in Python is an object, or so the saying goes. If you want to create your own custom objects, with their own properties and methods, you use Python’s class object to make that happen. But creating classes in Python sometimes means writing loads of repetitive, boilerplate code to set up the class instance from the parameters passed to it or to create common functions like comparison operators.

Dataclasses, introduced in Python 3.7 (and backported to Python 3.6), provide a handy, less verbose way to create classes. Many of the common things you do in a class, like instantiating properties from the arguments passed to the class, can be reduced to a few basic instructions.

Python dataclass example

Here is a simple example of a conventional class in Python:

class Book:
    '''Object for tracking physical books in a collection.'''
    def __init__(self, name: str, weight: float, shelf_id:int = 0): = name
        self.weight = weight # in grams, for calculating shipping
        self.shelf_id = shelf_id
    def __repr__(self):
            weight=self.weight!r, shelf_id=self.shelf_id!r)")

The biggest headache here is the way each of the arguments passed to __init__ has to be copied to the object’s properties. This isn’t so bad if you’re only dealing with Book, but what if you have to deal with  BookshelfLibraryWarehouse, and so on? Plus, the more code you have to type by hand, the greater the chances you’ll make a mistake.

Here is the same Python class, implemented as a Python dataclass:

from dataclasses import dataclass

class Book:
    '''Object for tracking physical books in a collection.'''
    name: str
    weight: float 
    shelf_id: int = 0

When you specify properties, called fields, in a dataclass, the @dataclass decorator automatically generates all of the code needed to initialize them. It also preserves the type information for each property, so if you use a code linter like mypy, it will ensure that you’re supplying the right kinds of variables to the class constructor.

Copyright © 2023 IDG Communications, Inc.

Source :

Leave a Comment

SMM Panel PDF Kitap indir